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Chlamydia trachomatis is an obligate intracellular bacterium that infects over 100 million people globally every year. Chlamydia infections can be persistent, cause infertility and blindness, adding an economical burden in the healthcare systems. Moreover, Chlamydia infections are treated with broad-spectrum antibiotics that contribute to the selection of antibiotic resistant bacteria in the commensal flora. For this reason, novel compounds with specificity against C. trachomatis would be important for treatment of Chlamydia infections.

We have developed a new class of substituted 2-pyridone amides that inhibited development of C. trachomatis. While bacterial growth was only affected to a limited extent, the produced progeny bacteria had impaired capacity to infect new cells. The compounds presented no toxicity in human or mouse cell lines and they did not inhibit growth of bacteria from the normal flora. Structure activity relationship (SAR) development of 2-pyridones lead to compounds with effect at nanomolar concentrations. Further modifications of the C3 part of the molecules resulted in isostere compounds with even a higher potency. By exploring the C8 position, we observed that methylsulfonamide substituents improved the pharmacokinetic properties and enabled oral uptake in mice. This discovery opens the door for oral treatment.

Among 2-pyridone amides, KSK213 was one of the most potent and we investigated the mode of action on the life cycle of C. trachomatis. KSK213 reduced transcription by the end of the developmental cycle and upon infection of new host cells. Mutations in RNA helicase and RNAse III genes, involved in transcription, mediated resistance to KSK213. It also attenuated the infectivity in a mouse vaginal infection model. To further explore the molecular target for 2-pyridone amides in Chlamydia, we used a custom synthesized probe for affinity chromatography approaches.

Here we show that 2-pyridones are potent non-toxic inhibitors of C. trachomatis that can be chemically modified to increase potency and enable oral bioavailability. These molecules have the potential to treat and prevent Chlamydia infections without affecting the normal flora.